The present invention is in the field of time delay devices, such as those that may be used for the control of phased-array radars, optical signal processing, and optical correlators.
In the original patent disclosure, we discussed a binary cell (and higher order exponential cells) for producing optical true time delays. One possible implementation is shown in FIG. 1. On the left is a micro-electromechanical (MEM) device, which in this case is an array of micro-mirror, each of which can tip to two different angles, xc2x1xcex8, with respect to the normal to the MEM plane and about a vertical axis. In the same plane as the MEM are an auxiliary mirror and a delay unit. The auxiliary mirror may require a stepped or sawtooth surface to properly image the tilted mirrors of the MEM. The delay unit in this disclosure will become a fiber array. There are two field lenses in front of the MEM plane. On the right we have two pairs of spherical mirrors. The center of curvature (CC) of each mirror is indicated in the figure.
Mirrors A, B, the auxiliary mirror and the MEM plane with a field lens form a White cell. To briefly review the operation, consider light traveling from Mirror B toward the MEM. Suppose every micromirror is tipped to xcex8. Then the light from Mirror B will return to Mirror A, from which it goes to the Auxiliary Mirror. Light bounces back and forth between B, the MEM, A, and the Aux. Mirror, and is reimaged to a new spot each time it strikes the plane containing the MEM and the auxiliary mirror. We will discuss the spot pattern shortly.
Now suppose that light strikes the MEM after coming from Mirror B, but this time the micro-mirror is tipped to xe2x88x92xcex8. This directs the light to Mirror E. From E the light goes to the delay unit. It returns from the delay unit, going this time to Mirror F, and then back to the MEM.
We have said that the light forms spots on the MEM plane. We now discuss the spot pattern with the help of FIG. 2. The figure shows the front of the MEM in the middle with the auxiliary mirror to the left and the entrance to the delay unit on the right. We show the spot patterns for three different beams. One beam is represented by the circles, one by the squares, and one by the triangles. The beams are input into the cell via an input turning mirror just below the Auxiliary Mirror. (These could be input via the MEM itself as discussed in other disclosures). Each beam forms a spot labeled xe2x80x9c0xe2x80x9d there. The input turning mirror is adjusted so as to direct the light to Mirror B. Mirror B images this spot onto the MEM, at a location that is an equal and opposite distance from Mirror B""s center of curvature (CC(B)). The new spot is labeled xe2x80x9c1xe2x80x9d is the first bounce.
If the micromirror is tipped to +xcex8, the light goes to Mirror A. Mirror A images the first spot, on the MEM, to a second spot on the auxiliary mirror. This appears an equal and opposite distance about A""s center of curvature. From the auxiliary mirror the light returns to Mirror B, thence to the MEM, and the process continues. Mirror B forms odd-numbered spots on the MEM and Mirror A forms even numbered spots on the auxiliary mirror.
Now suppose on a given odd-numbered bounce, the MEM micromirror is tipped to xe2x88x92xcex8. Now the light goes to Mirror E. Mirror E forms the next even-numbered spot, this time on the delay plane, which is a plane in the delay unit that is conjugate to the MEM. In the previous disclosures, light passing through a spot on the delay plane enters the delay unit, propagates some distance into the unit, and is reflected back to the delay plane, where it reforms a spot. For example, light striking the delay plane on bounce 2xe2x80x2 propagates for some time and returns back through spot 2xe2x80x2. In the present invention, the spots enter through some point 2xe2x80x2 and may exit at a corresponding point in the delay unit output plane. The spots have been discussed in previous disclosures as well.
The present invention includes a fiber optic delay unit, an apparatus for generating time delays in signals, and methods for optically generating time delays in signals.
In broadest terms, a delay unit for optically generating time delays in signals of the present invention comprises: a delay entrance plane and a delay exit plane. The delay entrance plane comprises at least one row of signal input positions. Each signal input position is adapted to receive an optical beam from a source. The delay exit plane comprises a respective number of rows of signal output positions. Each signal output position is adapted to output an optical beam received by the delay entrance plane. Each signal input position of a given row is connected by an optical fiber to a corresponding signal output position. Each optical fiber of a given row is the same length as every other optical fiber in that row.
An apparatus for optically generating time delays in signals of the present invention comprises an auxiliary mirror, a micro-electro-mechanical device, a delay unit, a first pair of spherical mirrors and a second pair of spherical mirrors. The delay unit used in the apparatus comprises: a delay entrance plane and a delay exit plane. The delay entrance plane comprises at least one row of signal input positions. Each signal input position is adapted to receive an optical beam from a source. The delay exit plane comprises a respective number of rows of signal output positions. Each signal output position is adapted to output an optical beam received by the delay entrance plane. Each signal input position of a given row is connected by an optical fiber to a corresponding signal output position. Each optical fiber of a given row is the same length as every other optical fiber in that row. Each mirror of the first pair of spherical mirrors has a center of curvature. Each mirror of the first pair of spherical mirrors is positioned such that its center of curvature lies between the auxiliary mirror and the micro-electro-mechanical device. Each mirror of the second pair of spherical mirrors has a center of curvature. Each mirror of the second pair of spherical mirrors is positioned such that its center of curvature (or the image of its center of curvature) lies between the micro-electro-mechanical device and the delay unit.
In a preferred embodiment of the present invention, the auxiliary mirror, micro-electro-mechanical device and the entrance and exit planes of the delay unit all lie in a first plane while the first and second pairs of spherical mirrors lie in a second plane. In another preferred embodiment of the present invention, the apparatus further comprises at least one optical element disposed between the first plane and the second plane.
A second apparatus of the present invention for optically generating time delays in signals comprises a micro-electro-mechanical device disposed in a first plane, an auxiliary mirror disposed in a second plane, the entrance and exit planes of a delay unit disposed in the second plane, and a pair of lenses disposed between the delay unit and the micro-electro-mechanical device. The delay unit of this second apparatus comprises: a delay entrance plane and a delay exit plane. The delay entrance plane comprises at least one row of signal input positions. Each signal input position is adapted to receive an optical beam from a source. The delay exit plane comprises a respective number of rows of signal output positions. Each signal output position is adapted to output an optical beam received by the delay entrance plane. Each signal input position of a given row is connected by an optical fiber to a corresponding signal output position. Each optical fiber of a given row is the same length as every other optical fiber in that row.
In a preferred embodiment, the apparatus further comprises at least one optical element disposed between the first plane and the second plane.
A method of the present invention for optically generating time delays in signals comprises the steps of: modulating an input signal onto an optical beam, passing the optical beam through an apparatus for optically generating time delays, and down-converting the optical beam to an output signal. The apparatus comprises an auxiliary mirror, a micro-electro-mechanical device, a delay unit, a first pair of spherical mirrors and a second pair of spherical mirrors. The delay unit comprises: a delay entrance plane and a delay exit plane. The delay entrance plane comprises at least one row of signal input positions. Each signal input position is adapted to receive an optical beam from a source. The delay exit plane comprises a respective number of rows of signal output positions. Each signal output position is adapted to output an optical beam received by the delay entrance plane. Each signal input position of a given row is connected by an optical fiber to a corresponding signal output position. Each optical fiber of a given row is the same length as every other optical fiber in that row. Fibers in each row may have a different length than fibers of any other row. Each mirror of the first pair of spherical mirrors has a center of curvature. Each mirror of the first pair of spherical mirrors is positioned such that its center of curvature lies between the auxiliary mirror and the micro-electro-mechanical device. Each mirror of the second pair of spherical mirrors has a center of curvature. Each mirror of the second pair of spherical mirrors is positioned such that its center of curvature lies between the micro-electro-mechanical device and the delay unit.
A second method of the present invention for optically generating time delays in signals comprises the steps of: modulating an input signal onto an optical beam; passing the optical beam through an apparatus for optically generating time delays; and down-converting the optical beam to an output signal. The apparatus comprises: a micro-electro-mechanical device disposed in a first plane; an auxiliary mirror disposed in the first plane; a delay unit disposed in a second plane; and a pair of lenses disposed between the delay unit and the micro-electro-mechanical device. The delay unit comprises: a delay entrance plane and a delay exit plane. The delay entrance plane comprises at least one row of signal input positions. Each signal input position is adapted to receive an optical beam from a source. The delay exit plane comprises a respective number of rows of signal output positions. Each signal output position is adapted to output an optical beam received by the delay entrance plane. Each signal input position of a given row is connected by an optical fiber to a corresponding signal output position. Each optical fiber of a given row is the same length as every other optical fiber in that row.